ACTION-1 phase Ib/3 trial of RYZ101 in somatostatin receptor subtype 2–expressing (SSTR2+) gastroenteropancreatic neuroendocrine tumors (GEP-NET) progressing after <sup>177</sup>Lu somatostatin analogue (SSA) therapy: Initial safety analysis.
Authors: Michael Morris, Gary A. Ulaner, Daniel M. Halperin, Jonathan R. Strosberg, Samuel H. Mehr, Daneng Li, Heloisa P. Soares, Lowell Brian Anthony, Sandy Diana Kotiah, Heather Jacene, Marianne E. Pavel, Pamela L. Kunz, Denis Vasconcelos Ferreira, Joanne Li, Kimberly Ma, Jessica Rearden, Susan Moran, Thomas A. Hope, Simron Singh
Journal: Journal of Clinical Oncology (2023)

4132 Background: RYZ101 ( 225 Ac-DOTATATE) is a first-in-class, highly potent alpha-emitting radiopharmaceutical in development for treating SSTR2+ solid tumors. Alpha-particles (as emitted by 225 Ac) have a shorter path length (40–100 μm) and higher linear energy transfer (80–100 keV/μm) than beta-particles, causing more frequent double-strand DNA breaks and potentially higher cancer cell kill rates and less damage to healthy tissues. ACTION-1 (NCT05477576) is a 2-part, global, randomized, controlled, open-label, phase 1b/3 trial of RYZ101 in patients (pts) with advanced well-differentiated SSTR+ GEP-NETs progressing after 177 Lu-SSA therapy. Part 1 (phase 1b) aims to determine safety, pharmacokinetics, and recommended phase 3 dose (RP3D) of RYZ101. Methods: Part 1 is an uncontrolled dose de-escalation study with a Bayesian optimal interval design. Escalation (0.197) and de-escalation (0.298) boundaries based on a target dose-limiting toxicity (DLT) rate of 25% were applied. Pts received RYZ101 IV every 8w for up to 4 cycles. Planned dose levels (n=6/level): Level 0 (starting dose), 120 kBq/kg (3.2 µCi/kg); if necessary, Level –1, 90 kBq/kg (2.4 µCi/kg); Level –2, 60 kBq/kg (1.6 µCi/kg). No dose escalation above starting dose was permitted. DLT was assessed for 56d after the first RYZ101 treatment. Treatment-emergent adverse events (TEAEs) were graded by NCI-CTCAE v5.0. Dose de-escalation decisions and safety data review were overseen by a Data Review Committee. Data cut-off: 26 Oct 2022. Results: At data cut-off, 9 pts had received RYZ101 at 120 kBq/kg (median dose 8.9 MBq); 7 pts were DLT-evaluable. No DLTs occurred and no dose de-escalation steps were implemented. Baseline characteristics: median age 70y; male (n=6)/female (n=3); ECOG PS 0 (n=4)/1 (n=5); median disease duration 6.9y; primary tumor site GI (n=6)/pancreas (n=3). A safety summary is shown. No treatment-related serious AEs were observed. TEAE requiring dose reductions occurred in 2 pts (Grade 2 platelet count decreased, n=1; Grade 2 thrombocytopenia, n=1). Grade 3 or 4 TEAEs occurred in 3 pts (lymphocyte count decreased, n=2; skin infection, n=1; weight decreased, n=1). One serious adverse event (skin infection) was unrelated to treatment. Conclusions: RYZ101 was well tolerated at 120 kBq/kg, which was declared the RP3D. Part 2 (Phase 3) will commence after Part 1 and will compare RYZ101 at the RP3D with standard of care in pts with advanced SSTR2+ GEP-NETs with disease progression following prior 177 Lu-labeled SSAs. Clinical trial information: NCT05477576 . [Table: see text]